A conventional radio-frequency anechoic chamber is constructed in such a manner that radiowave absorbers, each of which has the shape of a triangular pyramid or a serrate cone (deformed triangular pyramid), and is formed by laminating a plurality of sheets made of, for instance, foam polyethylene containing carbon at different contents, are provided for all inside of the peripheral walls and for the entire ceiling surface without a gap.
In radio-frequency anechoic chamber, the frequencies of the radiowaves which are presently used in the case of measuring electromagnetic compatibility, electromagnetic interference or the like fall within the range of about 30 MHz to 1000 MHz (a wavelength range of about 10 meters to 0.3 meter).
Therefore, the height of each of the radio-wave absorbers having the shape of the triangular pyramid or serrate cone (deformed triangular pyramid) arranged for all inside of the peripheral walls and the entire ceiling surfaces in a radio-frequency anechoic chamber needs to be set to a value from 1/2 to 1/4 of the maximum wavelength (from about 5 meters to 2.5 meters) of the radio wave. Since each of the radio-wave absorbers is large in size, the volume of the radio-frequency anechoic chamber must be large. Either is the area which is needed to construct the radio-frequency anechoic chamber.
On the other hand, it is economically difficult to provide a radiowave absorber which can completely absorb electric waves. The radiowave absorber which is generally used reflects a part of the radiowaves and the reflection effect differs according to the frequency of the radiowaves. Therefore, it is difficult to obtain a good frequency characteristic over a wide range.
Further, the presence of apparatuses or persons other than the EUP(equipment under test) in the radio-frequency anechoic chamber makes ignorable the influences which are exerted on the results of the measurement. Therefore, another room for isolating apparatuses (measuring equipment) other than the EUP and a room for persons need to be provided separately from the radio-frequency anechoic chamber. The existence of this room, thus, increases the construction cost and area.